1. Field of the Invention
The present invention is directed to capstan motors. More specifically, the present invention is directed to a capstan motor having a central rotatable shaft with a capstan and a drive armature located at opposite ends of the shaft along with shaft bearing supports.
2. Description of the Prior Art
In contemporary magnetic tape handling devices, a record medium such as a magnetic tape, is required to be moved past a magnetic transducer at a relatively high speed to accomplish either storage or read-out of information magnetically stored on the recording medium. Such data storage devices store or recover information only when the medium is traveling at a constant speed whereby the response of the storage system is a function of the ability of the system to accellerate and decellerate the recording medium and to maintain the operating speed of the recording medium at a preselected speed. Prior art devices have used capstan motors driving a tape drive capstan with intermediate mechanical drive elements interposed between the drive motor and the capstan. Such prior art devices are subject to torsional flexibility and cause unwanted oscillations and speed fluctuations at the capstan. Recent developments have been directed toward providing a combined capstan and motor structure which does not utilize any intermediate mechanism wherein the motor and capstan is an integrated construction. An example of such a prior art motor-capstan construction is found in U.S. Pat. No. 3,490,672. However, such prior art devices, while eliminating many of the problems associated with the intermediate mechanism between the motor and the capstan, still exhibit inherent problems which stem from dimensional differences between the rotatable shaft and the housing caused by temperature variations which dimensional differences affect the preload stress on the support bearings. Such preload stress variations result in large differences in the track followed by the ball bearing in a ball bearing raceway, which variations result in changes in the capstan run-out, or eccentricity, to produce unstable tape movements. Thus, such temperature differences which may be the result of ambient or previous immediate history of motor temperature conditions result in undesired driving conditions for the magnetic tape and cannot be reduced by a simple increase in the tolerances on capstan dimensional finishing.